Nowadays, microelectromechanical systems (MEMS) are widely used in a very large number of products (for example, inertial sensors in the automotive sector). In such systems, sophisticated mechanical structures primarily manufactured from silicon are combined with high-precision electronic circuits in order to implement diverse functions in miniaturized form.
Structures exposed to moving or mechanical stresses are often used in the above-named MEMS systems. In the case of sensor applications, inferences are made concerning various measured variables (for example, acceleration, rotation rate, pressure, etc.) from a vibration, shape, position, etc. of the structures. In actuator applications, the above-named properties are used for influencing the surroundings.
In order to be able to implement the described functions, the structures must be mechanically deformable. However, the deformable structures may generally experience both intended and unintended deformations and vibrations. The intended deformations and vibrations are necessary for the function, while the unintended deformations and vibrations are generated for physical reasons.
An avoidance, reduction or cessation of the character of the intended and unintended deformations and vibrations may account for a substantial share of a development effort. In this connection, mechanical properties of the silicon must be considered, silicon being mechanically very durable while having very low inherent damping. It is therefore important that the unintended deformations or vibrations be reduced or damped, in order to preferably prevent an impairment of the provided functionality.
The above-named optimization of the deformations and vibrations may be carried out with the aid of different technical means. It is known, for example, from DE 10 2009 045 541 A1 to provide mechanical stops for this purpose. The mechanical stops are, however, only effective in certain directions and only in critical amplitudes, but they do exert a substantial influence on the system, which may impair the function.
It is further known to use media (gases, vapors, liquids, etc.) for this purpose (see, for example, Stephen Terry, “A miniature silicon accelerometer with built-in damping,” Solid State Sensor and Actuator Workshop, Technical Digest, 1988, Hilton Head Island, U.S.A., pages 114-116). However, the media are also effective at still non-critical amplitudes; as a result, the selective damping of unintended vibration modes may only be implemented to a limited extent.
Furthermore, electrical and/or magnetic fields may be used for this purpose of exciting the micromechanical structures (see for example, Martin Handtmann, “Dynamische Regelung mikroelektromechanischer Systeme (MEMS) mit Hilfe kapazitiver Signalwandlung and Kraftrückkopplung (Dynamic regulation of micromechanical systems (MEMS) with the aid of capacitive signal conversion and force feedback), Dissertation, Technical University of Munich, 2002). The fields may control the deformations and vibrations at high precision; however, they are only functional in certain directions, extensive and fixed structures being required.
The management of the vibrations requires a dissipation of energy. In the case of stops, the energy is dissipated with the aid of a mechanical deformation; in the case of the above-named media, it is dissipated with the aid of current losses and in the case of the above-named fields, it is dissipated with the aid of counter-fields.
One form of energy dissipation is also proposed in the so-called “energy harvester” (see, for example, W. J. Choi, Y. Jeon, J.-H. Jeon, R. Sood, S. G. Kim, “Energy harvesting MEMS device based on thin film piezoelectric cantilevers,” Journal of Electroceramics, 2006, pages 543-548). In the devices proposed there, electrical energy is generated from selectively generated vibrations.
Without the above-named methods, errors may occur in the system, if, for example, overload, fatigue, non-linearity, irreversible displacement of the structures, etc. implement undesirable effects.